Re: Not able to understand how to write group by - Mailing list pgsql-general

afonit wrote
>> gender    participants       answer1_avg   answer2_avg
>> n                      3                     12                  3
>> m                      5                     4                  12
>> f                       7                    15                    23

Are you sure this is what you want?

Since there are two columns you will have to either use a CASE or a
sub-select to facilitate calculating the values for each of the columns.

SELECT gender, answer1_avg, answer2_avg
FROM (SELECT DISTINCT gender FROM ...) gn
LEFT JOIN (SELECT gender, answer1_avg FROM ...) ans1 USING (gender)
LEFT JOIN (SELECT gender, answer2_avg FROM ...) ans2 USING (gender)

You could also try learning "crosstab" from the "tablefunc" extension:

http://www.postgresql.org/docs/9.3/interactive/tablefunc.html

I do not see how a single "participant count" column will provide a
meaningful piece of data...

David J.






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